Urinary tract infections (UTIs) cause significant morbidity and are a major burdon on our healthcare system. Most UTIs are due to ascending infections by uropathogenic E. coli (UPEC) that leads to an inflammatory response in the bladder characterized by elevated urinary cytokines and apoptosis of superficial urothelial cells. We have previously observed that UPEC has a novel activity that suppresses activation of the inflammatory regulator NFKappaB, and we now demonstrate that clinical E. coli isolates and laboratory strains differentially induce multiple inflammatory genes and cytokines. Thus, our hypothesis is that UPEC encodes virulence factors that induce and modulate the host inflammatory response. In contrast to previous studies that examine one or a few strains in a single genetic background, this project will compare various E. coli strains that mediate acute disease as well as strains that induce benign conditions using urothelial cultures corresponding to normal patients and patients with benign conditions. By comparing E. coli isolates in a variety of host backgrounds in culture using ELISA to quantify cytokine secretion (Aim 1), we will establish the relative roles of pathogen and host in determining inflammatory responses. Aim 2 will define the diversity of genes that are modulated by UPEC and whether this modulatory activity is present in other E. coli strains of diverse clinical origin using real-time RTPCR to quantify inflammatory markers. In vivo analysis (Aim 3) using the mouse model will identify the role of specific cytokine responses in determining the course of infection for diverse E.coli strains by characterizing the timecourse of infection and severity of inflammation. Finally, using a genetic screen based on suppression of IL-8 expression, Aim 4 will identify the activity of UPEC that suppresses NFKB, provide initial characterization of its mechanism of action, and determine its conservation among E. coli strains of diverse clinical origin. This project will thus enhance our understanding of the roles of pathogen and host in infection and may lead to the identification of new therapeutic targets for the treatment and management of UTIs.